1. Field of the Invention
The present invention relates to a light amount adjustment device that is mounted in an optical device such as a camera or an interchangeable lens, and is also called a diaphragm device or the like.
2. Description of the Related Art
The performance of a light amount adjustment device (diaphragm device) as described above influences the quality of an image captured using an optical device. In particular, the shape of a diaphragm aperture (diaphragm aperture shape) which is formed by aperture blades and through which light actually passes changes the shape of a so-called blur or ghost. More specifically, when the diaphragm aperture shape is close to a circular shape, the shape of the blur or ghost also becomes circular and a high image quality is obtained. However, if the diaphragm aperture shape is a rectangular shape or flat shape greatly different from the circular shape, a blur or ghost appears with a similar shape and the image quality becomes poor.
A diaphragm aperture shape greatly different from the circular shape is readily generated when the diaphragm aperture is formed by two aperture blades that move linearly. To solve this, Japanese Patent Laid-Open No. 2012-78556 discloses a diaphragm device in which the diaphragm aperture is enlarged using four aperture blades that move linearly, and the number of corners of the aperture shape increases from that of a rectangular aperture shape, forming a polygonal diaphragm aperture shape closer to the circular shape than the rectangular shape.
In a light amount adjustment device using an iris diaphragm, which is known in Japanese Patent Laid-Open No. 2010-204693, a spacer is interposed between rectilinear aperture blades and swing aperture blades to prevent interference between the rectilinear aperture blades and the swing aperture blades and prevent inhibition of a smooth swing of the swing aperture blades.
However, in the arrangement of the diaphragm device disclosed in Japanese Patent Laid-Open No. 2012-78556, the shape of a light passage aperture is decided by only aperture blades that move linearly, so it is very difficult to form the light passage aperture into a desired aperture shape.
A light amount adjustment device using an iris diaphragm, like the device in Japanese Patent Laid-Open No. 2010-204693, uses a plurality of aperture blades, and it is very difficult to keep the moving postures of the respective aperture blades.